New findings indicate that the aurora and other
near-Earth space weather are driven by the rate at which
the Earth's and sun's magnetic fields connect, or merge,
and not by the solar wind's electric field as was
previously assumed. The merging occurs at a spot between
the Earth and sun, roughly 40,000 miles above the planet's
surface, and appears fundamental to the circulation of
particles and magnetic fields throughout near-Earth
space.
Researchers at the
Johns Hopkins Applied Physics Laboratory and the Air
Force Research Laboratory at Hanscom Air Force Base in
Massachusetts will announce the results of their study
today, Dec. 11, at the Fall American Geophysical Union
Meeting in San Francisco. The researchers, led by Patrick
Newell of APL, have developed a formula that describes the
merging rate of the magnetic field lines and predicts 10
different types of near-Earth space weather activity, such
as the aurora and magnetic disturbances.
"Having this formula is a big step forward for
understanding how the sun and Earth interact," Newell said.
And that understanding could help predict the space
weather that affects communications, navigation and the
health of humans in space.
The space between the Earth and sun is not empty but
filled with energetic particles, most of which are
generated in the solar atmosphere. Temperatures of a few
million degrees accelerate a stream of these particles,
called the solar wind, to roughly 1 million miles per hour.
Space weather scientists had long assumed that near-Earth
space weather phenomena could best be predicted by the
behavior of the solar wind electric field. However, Newell
and his colleagues were the first to put this theory to a
rigorous test with many data sets from a number of
years.
The team of researchers studied NASA satellite
observations of global auroral activity, NOAA satellite
observations of the stretching of the Earth's magnetic
field lines on the Earth's nightside and Air Force
satellite observations of the access of solar wind
particles to the Earth's upper atmosphere. They questioned
whether the electric field activity was really the best
predictor, or if each phenomenon would require its own
formula, and were surprised to learn that a single formula
— for the merging rate — gave the best clues to
the behavior of these 10 aspects of space weather.
George Siscoe of Boston University and Stanley Cowley
of Leicester University had previously suggested that the
merging rate would better explain near-Earth convection,
but Newell and his colleagues were surprised at how well
the single new formula works.
For a space scientist, the work is interesting also
because it provides the first strong empirical estimate of
the global merging rate. Boston University's Siscoe said of
the study, "It clearly represents a massive amount of work,
and it is undoubtedly an important contribution to the
subject of solar wind-magnetosphere coupling. People will
probably be discovering further implications of the formula
for years."
The research was funded by NASA and the National
Science Foundation.